Copying sheet

ABSTRACT

The invention relates to a copying sheet consisting of a base material or substrate having pressure or heat sensitive, opaque coatings of synthetic dispersions and softeners, preferably in combination with at least one stearate, wherein either the base material or the coating contains dyes or colored pigments that, on application of heat and/or pressure, make the characters impressed on the sheet readable.

O United States Patent 1 [111 3,725,107 Opderbeck et al. [451 Apr. 3,1973 54 COPYING SHEET 51 Int. Cl ..B4l:m 5/16, B41111 5/18 [75]Inventors: Fritz Opderbeck, Buederich Near Dusseldorf; Theodor Ploetz,Hoesel, [56] References cued $i g g fi gg gig UNITED STATES PATENTS3,167,443 1/1965 Melugh ..l17/36.7 [731 Asslgneei F Anlagen'ulm3,240,932 3/1966 Haines ..ll7/36.7 twllssesellschlfi beschflmktel'3,247,006 4/1966 Hoge et al. ..117/36.7 Haitung, Duesseldorf-Oberkassel,Germany Primary Examiner-Murray Katz 22 Filed; J 14 1971 Attorney-Kelman& Berman [21] Appl. N0; 153,025 57 ABSTRACT Related U.S. Application Dai The invention relates to a copying sheet consisting of [63]Continuation of Ser. N0. 809 949 March 24 1969 a base mater! substratehaving Pressure heat a sensitive, opaque coatings o syn e 1e lspersronsan abandoned, I f th t' d' d softeners, preferably in combination withat least one [30] Foreign Application priority Data stearate, whereineither the base material or the coat- 4 ing contains dyes or coloredpigments that, on applica- Mar. 23, 1968 Germany ..P 17 71 031.5 of heatand/Or pressure, k the characters i ressed on the sheet readable. [52]U.S. Cl. ..117/36.7, 117/155 VA, 260/27 R, p

260/41 C 5 Claims, No Drawings COPYING SHEET This application is acontinuation of Ser. No. 809,949, filed Mar. 24, l969 now abandoned.

Copying materials of the above-described type are progressivelyreplacing the heretofore customary means of producing copies, e.g.,carbon papers. These new copying materials have gained particularsignificance as a consequence of the expanding use of offree machines,computers, and other devices that require up to and more readablecopies.

All kinds of suggestions have been made regarding such copying sheets. Alarge group of these sheets is based on the following principle: acoating that consists of a large number of minute synthetic particlesand that is opaque due to light refraction at the grain boundaries ofthe individual particles or due to the included pores is deposited on adark-colored base material, thereby covering the dark-coloredbackground. Wax mixtures were originally used for this coating. Now,coatings of synthetic solutions or dispersions are common, because theyprovide better opacities and their mechanical and thermal properties aredesirable. However, the production of the opaque coating depends on veryspecific process conditions and on the medium from which the syntheticsolutions or dispersions are deposited on the colored base material.

In one process, for instance, the synthetic material is dissolved in asolvent and another organic liquid is added which mixes with the solventbut is not a, or only a poor, solvent for the synthetic. When thedeposited synthetic solution or dispersion is carefully dried, thesolvent evaporate first, then the synthetic flocculates or separates outand forms the opaque coating required for covering the dark-coloredbackground. On the other hand, in place of this system,solvent-non-solvent, oil-in-water, and water-in-oil emulsions of thesynthetics have proven particularly satisfactory. Among these are, forinstance, a solution of the synthetic in methylenechloride, to whichasmall percentage of water is added.

The effectiveness of such copying papers is based on the opaque coatingbecoming transparent at the point where pressure and/or heat is applied,for instance, by a pencil or the typewriter character, so that the darkcoloring of the substrate below it becomesvisible. Or, instead ofdarkening the base material by using, for instance, carbon black or agreen, blue or purple dye, one can add small percentages of dyes orpigments to the synthetic producing the opacity; these do notessentially affect the white color of the opaque coating, whileproducing a visible image when hit, for instance, by a typewritercharacter.

As'already mentioned, the technical requirements demanded of suchcopying sheets are very high. The required number of 15 andmore'readable copies can be supplied only if the opaque coating ishighly sensitive. On the other hand, this coating should not be sosensitive as to melt when exposed to slight mechanical stress or lowheat, e.g., when exposed to the sun or when stored in a tropicalclimate. Clearly, such requirements are really mutually exclusive,because a coating material so sensitive that the 15th copy is stillclearly readable implies a relatively low softening point.

Many attempts have been made to break this causal relationship betweensensitivity and insufficient heat resistance, but without success todate. It has been attempted to overcome this difficulty by adding enoughsoftener to the synthetic solutions or dispersions (among which themixed polymer of vinylchloride/vinylacetate, with predominant percentageof vinylchloride, has proven successful) to obtain just the requirednumber of copies without producing a heat sensitivity in the coatedsheet to the degree that it became totally black' during extendedstorage at slightly elevated temperature. This compromise is not asatisfactory solution.

Since excessive heat sensitivity is thus far one of the principalreasons barring general acceptance of the above described copying sheetsand their use in any climate, there is a great need for a copying sheetwith a coating that has a much higher softening point than the sheetswith opaque synthetic coatings .known to date and that still has thesame sensitivity to impact pressures or heat.

It has now been found, surprisingly, that the technical problem hereindiscussed can be solved by abandoning the previous attempts to find newand more suitable synthetic solutions or dispersions mixed withsofteners and following an entirely new course. The copying sheet of thepresent invention consists of a base materialsuch as paper with apressure and/or heat sensitive opaque coatings of synthetic solutions ordispersions and-softeners, preferably in combination with at least onestearate, wherein either the base material or the coating contains dyesor colored pigments which make the characters impressed on the coatingreadable when heat and/or pressure are applied and wherein the coatingcontains about 5 to 50 percent by weight of a modified rosin ester.'Thepreferred range is about 10 to 30 percent by weight.

More particularly, the coating compositions of the present inventioncontain (without reference to solvents or water) about 30 to percent,and preferably 40 to 50 percent, by weight of mixed polymers orsynthetics; about 5 to 50 percent, and preferably 10 to 30 percent, byweight of the rosin component; about 10 to 35 percent, and preferablyabout 20 percent, by

weight of softener; and, about 5 to 30 percent, andv preferably 10 to 20percent, by weight of stearate (e.g. aluminum stearate).

The softening point of such coatings can be raised by about 20 C byincluding the rosin ester of the present invention in the coatingmaterial, i.e., from the current softening point of about 60 C to C andhigher. And the addition of such modified rosin ester has the particularadvantage of permitting a reduction of the coating softener percentage,which, currently, is up to 45 percent byweight, by one-half. Since thesesofteners are relatively expensive to produce, this reduction representsconsiderable economic and technological progress. The percentage ofsoftener in a coating in accordance with the present invention andconsisting of synthetics, rosin ester, softener and at least onestearate is only 10 to 35 percent by weight, preferably around 20percent by weight. g

The stearates used together with softeners in such coating materials forcopying sheets assist in the emulsification (particularly withwater-in-oil emulsions), and improve the flow characteristics,- of thesynthetics. Normally, a stearate of a bivalent metal, particularlycalcium stearate, is used. For the copying sheet of the suitable and itis used in an amount between about 5 and 30 percent by weight of theentire coating. Most suitable are those coatings with about to 20percent by weight of aluminum stearate.

The raising of the softening point of the coating by 20 C and more,while retaining the same copying sensitivity, affords, in the copyingsheets of the present invention, the opportunity of using a highpercentage of stearates. This has, in turn, the advantage of greatlybroadening the coating melting temperature range. Currently availablecoatings with about 4 to 8 percent stearate have a melting range ofabout 58 C to 60 C, while those of the present invention with apreferred content of about 10 to 20 percent by weight of aluminumstearate have a melting range of 75 to 87 C. The raising of thesoftening point by 17 C was, thus, accompanied by a broadening of themelting range from about 20 to 12 C. The advantage of such a broadmelting range is that the copying sheets of the present invention donot; like the currently available ones, become completely black becausethe specified storage temperature is slightly or temporarily exceeded.

The modified rosin esters used in accordance with the invention arederivatives of natural rosins, particularly those from coniferous woods,the essential constituent of which is abietic acid, and particularlyafter processing with acrylic acid, maleic acid and esters of theseacids. They are additionally esterified with polyhydric alcohols likeglycerol, trimethylolproponol or pentacrythritol and are sold, forinstance, under the trade names Laropal and Alresat.

Typical examples of copying sheets made according to the presentinvention are produced as follows:

EXAMPLE I A wood-free 40 gram paper is dyed black in a printing press.0n this dark-dyed base material is deposited a coating compound made asfollows:

A mixture consisting of 500 parts by weight vinylchloride-vinylacetatemixed polymer with 15 percent of vinylacetate content 15.0 parts byweight Alresat 967C (rosin modified with acrylic acid) 6.2 parts byweight castor oil 7.4 parts by weight trioctylphosphate 7.4 parts byweight diisotridecylphthalate l4.0 parts by weight aluminum stearate Iis dissolved in 700 parts by weight of methylene chloride. To thissolution are added 200 parts by weight of water and the mixtureemulsified. This emulsion is deposited on the base paper by means of aroller coating fixture and this is done in such quantity that thecompleted copying sheet has, after careful drying at 55 C, a coatingof'8 to 10 gram/m In the examples 2 to 4 the same method of operation isused as described in Example I, while the composition of the coatingcompound is changed:

EXAMPLE 2 A mixture of 50.0 parts by weight vinylchloride-vinylacetatemixed polymer with percent vinylacetate content 30.0 parts by weightAlresat 967C" (rosin modified with acrylic acid) 2.8 parts by weightcastor oil 3 .6 parts by weight trioctylphosphate 3.6 parts by weightdiisotridecylphthalate 10.0 parts by weight aluminum stearate isdissolved in 900 parts by weight of methylene chloride. To this solutionare added 270 parts by weight of water and the mixture emulsified.

EXAMPLE 3 A mixture of 400 parts by weight Vinoflex 452(vinylchloridemaleic acid ester mixed polymer with 20 percent maleicacid ester content) 10.0 parts by weight Albertol l 1 1L (modifiedphenol resin) 8.6 parts by weight castor oil 10.7 parts by weighttrioctylphosphate 10.7 parts by weight diisotridecylphthalate 20.0 partsby weight aluminum stearate is dissolved in 900 parts by weight ofmethylene chloride. To this solution are added 270 partsby weight ofwater and the mixture emulsified.

EXAMPLE 4 A mixture of 40.0 parts by weight Vinylite VAGl-I (mixedpolymer of vinylchloride, vinyl acetate and other components) 20.0 partsby weight Alresat 945C (rosin adduct) 5.6 parts by weight castor oil 7.2parts by weight trioctylphosphate 7.2 parts by weightdiisotridecylphthalate 20.0 parts by weight aluminum stearate isdissolved in 1,000 partsby weight of methylene chloride. To thissolution are added 450 parts by weight of water and the mixtureemulsified.

What is claimed is: 1. In a copy sheet consisting of a paper basematerial, a normally opaque coating on said base material, and

- coloring matter interposed between said coating and said basematerial, the color of said coating being different from the color ofsaid coloring matter, the opaque coating obscuring said coloring matter,said coating responding to applied pressure by becoming sufficientlytransparent to reveal said coloring matter, the improvement in thecomposition of said coating which essentially consists of:

l. 30 to percent by weight of a copolymer of vinyl chloride and vinylacetate;

copolymer;

3. 5 to 30 percent by weight of a stearate of calcium or of aluminum;and

4. 5 to 50 percent by weight of a modified rosin ester,

5. the amount of said modified rosin ester being sufficientsubstantially to raise the temperature at which said coating becomestransparent in the absence of applied pressure.

2. In a sheet as set forth in claim 1, the amount of said rosin esterbeing between 10 percent and 35 percent by weight.

3. In a sheet as set forth in claim 1, said stearate being aluminumstearate.

10 to 35 percent by weight of a plasticizer for said I 4. In a sheet asset'forth in claim 3, the amount of said aluminum stearate being aboutto percent by weight.

5. In a sheet as set forth in claim 4, the amount of said copolymerbeing between about 40 percent and 50 5 percent, the amount of saidplasticizer being about 20 percent, and the amount ofvsaid modifiedrosin ester being between about 10 percent and percent.

2. 10 to 35 percent by weight of a plasticizer for said copolymer;
 2. Ina sheet as set forth in claim 1, the amount of said rosin ester beingbetween 10 percent and 35 percent by weight.
 3. In a sheet as set forthin claim 1, said stearate being aluminum stearate.
 3. 5 to 30 percent byweight of a stearate of calcium or of aluminum; and
 4. 5 to 50 percentby weight of a modified rosin ester,
 4. In a sheet as set forth in claim3, the amount of said aluminum stearate being about 10 to 20 percent byweight.
 5. In a sheet as set forth in claim 4, the amount of saidcopolymer being between about 40 percent and 50 percent, the amount ofsaid plasticizer being about 20 percent, and the amount of said modifiedrosin ester being between about 10 percent and 30 percent.
 5. the amountof said modified rosin ester being sufficient substantially to raise thetemperature at which said coating becomes transparent in the absence ofapplied pressure.